Siderophores are low molecular weight iron chelators produced by bacteria to scavenge iron from the environment, and are frequently required for bacterial virulence. The long-term goal of the research in this laboratory is to provide a detailed mechanistic and structural understanding of enzymes in the siderophore biosynthetic pathways that are targets for drug discovery. Toward that end, we propose to investigate the nonribosomal peptide synthetase accessory enzymes that are involved in the production of the siderophores pyochelin and pyoverdin from the bacteria P. aeruginosa. Two of the four enzymes to be studied, the isochorismate synthase (PchA) and isochorismate-pyruvate lyase (PchB), are ideal model systems for making fundamental advances in understanding alternate reaction pathways for catalysis. The studies of the ornithine hydroxylase (PvdA) show promise for novel flavin biochemistry, and the first characterization of the hydroxyornithine transformylase (PvdF) is proposed. We will use a multifaceted approach that includes enzyme kinetic analysis, structural biology and computational enzymology. Narrative Pseudomonas aeruginosa is a dangerous pathogen that is a common cause of infections in susceptible hosts, including cancer and AIDS patients, those with immune deficiencies, cystic fibrosis patients, burn patients and other at risk individuals including infants. The goal of this work is to provide a fundamental understanding of four enzymes that promote virulence in P. aeruginosa so that this information can be exploited to generate new antimicrobial drugs.